Of alhaffibra



' metal chromates Patented Apr. 16, 1929.

UNITED STATES PTENT @tFFlQE.

JOSEPH T. TERRY, on ALHAMBRA, CALIFORNIA, ASSIGNOR T0 CORDELIA E. TERRY,

\ or ALHAMBRA, camronnm.

CONCENTRATION OF OXIDIZED ORES.

No Drawing.

This invention relates to a process of treating ores and other metal bearlng materials. It is an object of this 1nvent1on to provide a process which is simple, efficient and otsufficient economy to render concentration practicable.

My invention is based on my discovery that chromium salts of metallic elements substantially insoluble in the solutions employed are susceptible to flotation concentration and also that lead, zinc, silver, b.is muth and mercury minerals are converted to substantially insoluble chromium derivatives by treatment with solutions oil" alkali. or alkali earth metal chromates alone orin conjunction with other reagents.

My process contemplates briefly the Slll)]QC- tion of the metalliterous material to the action of the water soluble chromates, such as sodium chromate or bi-chromate in neutral solutions or in conjunction with a neutral salt such as sodiumchloride or an alkali such as caustic soda or alkaline compounds such as sodium carbonate, sodium silicate, aqua-ammonia or an acid such as sulphuric, hydrochloric or acetic acid, to convert the metal or metals at least in part to chromium compounds substantially insoluble in the solution employed. Only a partial conversion or superficial surface filming ot the metalliferous particles is necessary for the success of my process. The part thus treated may then be subjected to any preferred method of froth flotation for the concentration and recovery of a concentrate containing chromium and other metal or metals associated therewith.

It is another object of my invention to treat ores containing two or more metals in such a manner as to first recover one of them by any suitable or preferred method, and then to recover the other metal or metals by the use of my treatment with chromatcs, or first with chromate to remove one of the metals and thento remove the other metal or metals in any suitable or preferred method, and in this manner, efiect a separation as well as aconcentration of metal bearing ores.

With the above and other objects in view, which will appear as the description proceeds, my invention consists in the steps of the process hereinafter described.

Assuming that an ore containing lead and Serial No. 71,019.

zinc both in the form of carbonates is to be treated, the ore is first ground to mesh screen or liner, water is added to the ground oreand the. mixture is rendered alkaline by the addition oil. any suitable base such as sodium hydroxide or salt having an alkaline reaction such as sodium carbonate, using approximately grams of sodium hydroxide to 1 liter otwatcr. To the mixture is now added sodium chromate Na ca-0,. The quantity of the latter will vary, depending upon the richness of the ore, but 1 gram to a liter is ordinarily sutficient. The proportion oi the ore to the water one part to four, the reaction takes place promptly, the sodium chromatic combining with the lead and zinc in the ore, forming a corresponding chromate in accordance with the following chemical equation:

It will be understood that a mere filming action is necessary in this process. At ordinary tempera-tine the reaction is complete in about one-halt hour, but heating the mixture facilitates the reaction, for instance, heating to 180 F. will complete the reaction in about live minutes. The mixture is now conveyed to a ili'roth flotation tank of any suitable or preferred construction, and subjected to a froth flotation agent such as ortho-toluidine. This flotation reagent will float the lea d chromate only, leaving the zinc chromate unaffected. The remaining pulp now treated with a :t'roth flotation agent; consisting oi oleic acid and distillate, which will float the zinc chromate.

The liquid containing considerable quan-.v

tities of unused sodium chromate is now decanted from the pulp, rcstandardized to make up the deficiency in sodium chromate and sodium hydrate and used in the treatment of another batch of ore,

As a modification of the above process in the treatment an ore containing lead and zinc, whether inthe form of carbonates or any other salt or oxide, the ground pulp is acidulated with sulphuric acid, using 2 c. c. of sulphuric acid to the liter of water and using2 grams of sodium chromate to the liter. In this acid solution the sodium chromate will react with the lead only, forming lead chromate and leaving the zinc unafi'ected. The mixture is then treated in the ing metal sulphides.

flotation tank with a flotation agent such as oleic acid and carbon bi-sulphide or cresylic acid and distillate. After the removal of the lead chromate by flotationthe pulp containing the zincis rendered alkaline by the addition of sodium carbonate or sodium hydroxide when the sodium chromate will attack the zinc and form zinc chromate, which may then be floated by mixture of oleic acid and distillate.

As a third modification of the treatment of the lead and zinc ore just referred to, the ground ore may first be treated with sulphuric acid sufficient in quantity to com- 'bine with all the zinc in the ore to form zinc sulphate. The lead will :torm insoluble lead sulphate. The ZlIlC sulphate in solution is decanted and the pulp containing now the lead alone is treated with sodium chromate to film the same with lead chromate, which may then be removed in the froth flotation tank by flotation agents such as oleic acid a d carbon bi-sulphide or resylic acid and distillate.

If the lead and zinc ore should contain silver, the latter combined with the lead, then the silver will be recovered. together with the lead chromate, as described in the preceding orocesses. However, it the silver is in the orm of silver carbonate and not combined with the lead, then it will form silver chromate and. be recovered together with the lead chromate.

' Ores containing bismuth or mercury may be treated in the same manner with sodium chromate in alkaline solutions, forming the corresponding bismuth chromate and mercury chromate are recovered by flotation.

My chromate filming process is applicable, as mentioned before, to all ores other than sulphides. Sulphides are not included be cause they are floatable'as such, and therefore require no treatment. However, I have found that a more effective extraction of the metal content of? some ores is obtained by treating the ores in an acid or alkaline solutionwith a chromate solution to form the corresponding metal chromate at least in part, and then by treating the mixture with an agent such as sodium sulphide or hydrogen sulphide to form the correspond- As well known, the metal sulphides are exceedingly floatable by well known froth flotation methods and with some oresit may be economical because of the more effective recoveryot the metal contents to use this modification oi the process as explained, to-wit, first forming the metal chromate at least in part, and then the corresponding metal sulphide, which is thenrec'overed by froth flotation.

Another modification is to use sodium chromate in ammonical solutions in the treatment of zinc minerals otherthan sulphides. The ammonia of the solution appears to attack the zinc so that the latter is instantly filmed with the zinc chromate and may then be recovered by froth flotation with oleic acid and distillate. The use of ammonical solutions is also advantageous in the treatment of lead minerals other than sulphides, but it is especially useful for zinc minerals.

In a similar manner ores other than sulphides containing bismuth, silver and mercury may be treated with chromate solutions to form a chromium derivative at least in part, so as to render the metal values floatable by well known froth flotation processes.

Any soluble chromate may be used, but naturally sodium bi-chromate will be employed because of its low cost. It is of course understood that a base such as sodium hydroxide added to a bi-chromate solution converts it into the normal chromate.

Another modification of my process relates to the treatment of lead sulphide (galena) associated with lead carbonate and'iron sulphides (pyrites). The ground ore pulp is irst treated in the flotation tank with a suitable reagent suchas a mixture of pine oil and carbon bi sulphide, which will float the lead sulphide and leave the lead carbonate and iron pyrites unatl'ected. After the removal of the concentrate of lead sulphide the ore pulp is rendered alkaline and sodium chromate is added, thereby forming lead chromate, at least in part, the iron pyrites remaining unaffected and the pulp is then submitted to froth flotation by the same or other suitable reagents to recover the lead carbonate.

lethods have been known before in which ores containing lead minerals were treated to form a superficial film of lead chromate and treating the same with an organic substance to oxidize the latter and precipitate the oxidation products on the particles of the lead minerals. lliiy process difl'ers therefrom in subjecting the finely ground ore pulp, which has been treated .with a chroinate solution, at once without any oxidation process to a froth flotation.

Various changes in the steps of the process may be made by those skilled in the art without departing from thespirit of my in:

2. A process of treating ores other than sulphides,and containing lead, zinc, silver,

mercury and bismuth, either singly or in combination, comprising subjecting the finely ground ore pulp-n to a chromate solution to form the corresponding metal chromium derivative at least in part and directly treating the ore pulp with a. selective froth flotation agent to separately concentrate and recover the metals affected by the chromium treatment.

3. A process oftreating ores other than sulphides, and containing lead, zinc, silver, mercury and bismuth either singly or in combination, comprising subjecting the finely ground ore pulp to an alkali metal chromate solution to form the corresponding metal chromate at least in part, and directly treating the ore pulp by a froth flotation process to concentrate the metal or metals affected by the alkali metal chromate treatment.

4. A process of treating ores other than sulphides and containing lead, zinc, silver, mercury and bismuth either singly or in combination, comprising subjecting the fine- 'ly ground ore pulp to a chromate solution acid in reaction, thereby forming the corresponding metal chromium derivative at least in part of the metals capable of reacting with the chromate solution in an acid medium, treating the ore pulp by a flotation process to concentrate and remove the metal chromate derivative, renderin the ore pulp alkaline in reaction thereby forming metal chromium derivative of a metal capable of reacting with the chromate solution in an alkaline medium and directly treating the pulp by a froth flotation process to concentrate the metal chromium derivative thus formed.

5. A process of treating ores other than sulphides containing lead and Zinc comprising treating the ore pulp with a chromate solution to form lead chromate at least in part and directly treating the pulp by a froth flotation process to concentrate and remove the lead chromate derivative.

In testimony whereof I have signed my name to this specification.

JOSEPH T. TERRY. 

